1. Field of the Invention
This invention relates to pumps, and particularly to pumps wherein fluid pressures must be sealed from escape around pump drive shafts, such as with rotary pumps of the centrifugal type.
2. General Description of the Prior Art
A principal cause of failure with centrifugal pumps is seal failure, that is, leakage by deterioration or destruction of shaft seals between the outside and inside of a pump housing. Shaft seals typically employ two frictionally engaging seal members, one of which is held stationary and seals to the pump housing, and the other sealably engages the pump shaft and rotates with and seals to it. In order to perfect the seal, some form of force must be applied to urge one of the sealing members against the other while they relatively rotate. Generally, if not in all cases, the shaft seal member is spring biased against the stationary sealing member. A spring force being a relatively constant force must be selected to provide sufficient force to effect a seal with maximum pump fluid pressures present, and, as a result, it is typical to provide a rather substantial spring force. This in turn, of course, effects a substantial friction between the sealing members, and if the pump is accidentally run dry, then one or both of the sealing members will most likely be damaged.
It is an object of this invention to provide an improved pump seal assembly wherein a variable bias is applied to sealing members, and thereby their life substantially extended.